"I would disagree because our definitions are different. Morality is defined by God and includes many things most nonchristians I know find okay to do. Some of these include, but are not limited to, lustful thoughts, white lies, porno, etc...."
I'm not sure whether considering certian acts sins or not is relevant if those acts are committed with the same frequency by christians and non-christians alike. There is no proof christains sin against god's will any more or less than the rest of the population, apart from anecdotal evidence.
Furthermore, while the christian and non-christian may have disagreements on what is a sin, so do christians among themselves. Here's an easy example - alcohol. Many denominations clearly think its a sin to ingest any amount of alcohol for any purpose, whereas others drink wine as part of their religious observance (let alone moderate, social drinking). Both are saved christians, yet both have opposite views on whether the act is a sin against God. They both can't be right. This is but one example, which ranges from the benign to the extreme - the list goes on and on.
"I would say motivation. The christian should, if strong in their christian walk, have no desire to commit sin. This is addressed in romans 8."
Desire, or intent to do the act, is a necessary element to the commission of a sin. The act, coupled with that intent, is either a sin or it is not. But since there is divergence among christians themselves as to what constitutes a sin to begin with, it seems like this can be easy standard to meet. For example, if I wanted to be a saved christian, but still enjoy a beer on a hot summer day, then I'd be better off a Catholic than a GRB Baptist, wouldn't I? As a Catholic, there wouldn't be anything wrong with having a beer, let alone the desire to drink one.
"Because just because it is "paid for" doesn't make it any less immoral."
I take this to mean you disagree with Lewis' statement that immoral acts require a consequence in order for it to be immoral at all. For example, if there was a person designated to go to jail for me if I broke the law, is it still accurate to say there are any real consequences to me for doing that which is wrong? I understand the salvation concept, but saying Jesus suffered the consequences for others' sins is in direct refutation of Lewis' statement about the very nature of morality from God.
In other words, an act is immoral according to god just because he says so, and even tho the individual who committed the act will never suffer any consequence from God for committing that act? Or another way...what does God do to those who commit sins? If he does nothing, then is the act a sin just because god proclaims it to be so?